The proposed ethnographic study seeks to investigate the nature of changes in the lives of Mexican gay and bisexual male immigrants that result in increased HIV risk. This study builds on previous quantitative research with Latino gay and bisexual men that paradoxically found that recent immigrants have much lower levels of HIV risk than their U.S-born counterparts, and that their risk increases with their length of residence in the US. The proposed study's specific aims are: (1) To describe the processes of incorporation into US gay life among Mexican gay and bisexual male immigrants and how their participation in social and sexual contexts in the United States affects their sexual health and HIV risk; (2) to compare the Mexican gay and bisexual immigrants' lived experiences regarding sexuality and HIV risk with those of their US-born counterparts; (3) to advance our theoretical knowledge about the emergence of health risks out of the intersection of migration, sexual orientation, participation in US social settings, and social inequality; and (4) to generate and disseminate data that HIV educators can directly use to design and improve HIV prevention programs for gay and bisexual Mexican immigrants. The study will consist of individual qualitative interviews with 150 men (2.5 hours per interview on average), follow-up interviews twelve months after the initial interview (1.25 hours per interview on average), and twenty-seven months of participant observation in social settings (Latino and non-Latino, gay and heterosexual) where gay and bisexual Mexican immigrants participate (4,360 hours of participant observation projected). These research activities will be conducted in San Diego, California. The collected textual data (field notes and interview transcripts) will be systematically coded for analysis. In broadest terms, the proposed research rejects monolithic conceptions of ethnic communities and contributes to the larger effort to study cultural diversity within ethnic minority communities in the US and the influence of such internal diversity on health. In this particular study, we focus on migration that is motivated by a homosexual orientation and seek to elucidate how it influences intra-group diversity in Latino communities in terms of sexuality and sexual identities, sexual behavior, participation and incorporation in US social settings, and sexual health.